1. Field of the Invention
The present invention mainly relates to an image forming apparatus, such as a color laser printer, a color copy machine and a color facsimile, adopting an electrophotographic process.
2. Description of the Related Art
In an image forming apparatus adopting an electrophotographic process, a toner as a developer develops a latent image, and the latent image is transferred and fixed on a recording material such as print paper to form an image. To particularly form a color image in the image forming apparatus, toner images of a plurality of colors (yellow, magenta, cyan and black) are primarily transferred and superposed on an intermediate transfer unit, and then the toner images are secondarily transferred all together to the recording material in a generally known configuration. An example of a known method of collecting a residual toner remained on the intermediate transfer unit after the transfer of the color image to the recording material includes a method of collecting the residual toner from the intermediate transfer unit after electrical charge by a cleaning charge roller. A high voltage needs to be applied to applied members for the primary transfer, the secondary transfer and the charge of the residual toner, and a dedicated power circuit and a current detection circuit that detects a current value may be arranged for each applied member. In this case, the power circuit and the current detection circuit are independently arranged for each applied member, and there is a problem of an increase in the cost due to an increase in the number of components. Another problem in an increasingly downsized image forming apparatus is an increase in a mounted area of the circuits associated with the increase in the number of components.
In a system proposed by Japanese Patent Application Laid-Open No. 2001-242723, a plurality of transfer units as applied members share a current detection unit to reduce the number of detection circuits.
However, further downsizing of the image forming apparatus is demanded. A further reduction in the power circuits and the current detection circuits as well as a reduction in the circuit mounted area are demanded. The effect of the sharing of the current detection circuit by the plurality of transfer units proposed in Japanese Patent Application Laid-Open No. 2001-242723 is limited in a rotary-system image forming apparatus that includes only one transfer unit.